Teens lose bone density after weight-loss surgery

NEW YORK (Reuters Health) - Teenagers who undergo gastric-bypass weight-loss surgery lose bone in the 2 years following the procedure, a new study shows.

"The good news is they started out with bones that were far heavier than normal," said Dr. Thomas Inge, a researcher in the study and an associate professor of pediatrics and surgery at Cincinnati Children's Hospital Medical Center.

"After that (bone) loss, they end up about normal for their age," he told Reuters Health.

The long-term effects of the bone loss - and whether it levels out -- are unknown.

Inge and his colleagues measured the bone density, or bone hardness, of 61 teens who underwent the most common form of gastric bypass surgery.

The procedure reduces the stomach to a small pouch and diverts food around part of the small intestine. Less food is absorbed and the individual feels full sooner, leading to weight loss.

Inge estimates that up to 2,000 gastric bypass surgeries are done each year in teens. More than 200,000 U.S. adults had the surgery in 2009.

Bone density contributes to the strength of the bones; and their density changes in response to body weight and to weight-bearing exercise. In general, as people age, their bones become less dense.

The researchers took bone scans of the teenagers every few months after the surgery for 2 years.

On average, each patient lost nearly 200 grams of bone (about seven ounces, or the weight of a large apple) by the end of the study. That equaled seven percent of their starting bone mass, they report in the journal Pediatrics.

"What was reassuring was (bone density) didn't fall below the normal range" for teenagers, Dr. Anne-Marie Kaulfers at the University of South Alabama, and another of the study's authors, told Reuters Health.

Inge said that the loss was expected.

"When you load the skeleton with higher loads, it responds with greater bone density," he said. As the load lightens after weight loss surgery, the bones respond by becoming lighter as well.

Studies in adults have found that bone loss stabilizes three years after weight loss surgery.

The use of weight loss surgery in adolescents is controversial because there are few long-term studies of its effects years on.

Inge said his group intends to follow the patients for a total of 10 years.

"There is no data right now to say the risk of bone loss is greater than the risk of not doing the surgery," Dr. Mary Brandt, director of the adolescent bariatric surgery program at Texas Children's Hospital, told Reuters Health.

Brandt said that children who undergo weight loss surgery suffer from myriad weight-related health problems.

Among the teenagers in Inge's study, for instance, three out of 10 had high blood pressure, six out of 10 had sleeping problems, and one out of 10 had type-2 diabetes.